1. Field of the Invention
The present invention relates to a charging device for a portable electronic device battery and especially a portable phone battery adapted to charge a rechargeable battery housed in a portable phone.
2. Description of the Related Art
Conventionally, a charging device for portable phones to charge a rechargeable battery housed in a portable phone by using a dry battery as a power source is available. In the conventional dry battery-type charging device, a 4.5v or 6v power source made up of, for example, three or four AA batteries or three or four AAA batteries serially connected to one another is connected directly to a rechargeable battery housed in the portable phone to charge the rechargeable battery at a charging voltage of 4.5V or 6V, or a power source made up of, for example, two AA batteries or two AAA batteries serially connected to one another with its voltage boosted up to about 5V is used to charge a rechargeable battery housed in the portable phone at a charging voltage of about 5V.
A capacity of a lithium-ion battery housed in a recently-available portable phone is made larger in response to the expansion and sophistication of functions of the portable phone and, therefore, the use of a charging device made up of two or four AA or AAA batteries serially connected to one another is effective to achieve efficient charging of the lithium-ion battery.
The conventional dry battery-type charging device has a disadvantage in that, due to its large outside shape, it is of little practical use for portably carrying the charging device to achieve efficient charge of the rechargeable battery. Another disadvantage is that, when a supply voltage of the rechargeable battery in the portable phone drops to a level at which a telephone speech is disabled, the supply of currents from the dry battery having a high internal resistance to simultaneously meet the needs for both charging of the rechargeable battery in the portable phone and operations of functions of the portable phone is difficult and that the instant use of the function of a portable phone whose battery has become exhausted is impossible. Still another disadvantage is that the dry battery cannot be reused once it has been discharged, causing great loads on the environment and, therefore, new dry batteries have to be prepared to be used as a charging device for the portable phone.
A secondary battery pack system for a portable phone using a secondary battery instead of a dry battery is disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2004-112909). However, it is impossible for even the disclosed secondary battery pack system to be instantly used for the portable phone whose battery has been exhausted.
Also, a charging device for a portable phone using a lithium-ion battery that can instantly use a function of the portable phone whose battery has been exhausted is disclosed in Patent Reference 2 (Japanese Patent Application Laid-open No. 2006-141187). However, in the disclosed charging device, the charging mechanism of the lithium-ion battery in this charging device is included in the charging device and, as a result, the charging device is lacking in portability. Also, in the disclosed charging device, a protecting circuit to prevent the overdischarge, overcharge, and flowing of overcurrents in the lithium-ion battery is embedded, however, the protecting circuit is configured to protect the lithium-ion battery and not to prevent a failure and/or malfunction of an entire circuit and, therefore, the use of the lithium-ion battery only by the protection to be performed by the protecting circuit is also lacking in reliability. Moreover, in some cases, the protecting circuit does not operate for a time period for which the protecting circuit fails to respond thereto, however, in the above Patent Reference 2, the measure against this problem to be taken for the protecting circuit is not described.